HIGH ENERGY-EFFICIENCY BUILDINGS · 2017. 2. 6. · The 4th international Symposium on HVAC Beijing, China, October 9-11, 2003 1 HIGH ENERGY-EFFICIENCY BUILDINGS Ettore Zambelli*,

The 4th international Symposium on HVAC

Beijing, China, October 9-11, 2003

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HIGH ENERGY-EFFICIENCY BUILDINGS

Ettore Zambelli*, Marco Imperadori, Gabriele Masera

Department of Built Environment Science and Technology (BEST)Politecnico di Milano, via Bonardi 15, 20133 Milano - Italy

e-mail: [email protected], [email protected], [email protected]

Massimo Lemma

Istituto di Disegno e Architettura Urbanistica (IDAU)Università Politecnica delle Marche, via Brecce Bianche, 60131 Ancona - Italy

e-mail: [email protected]

ABSTRACTIn cold, central European climates, hyper-insulated, heat-conserving buildings have proven a very effective way to

reduce current energy consumption to 1/10th of a traditional house. Using dry, stratified building techniques (Str/En)allows to obtain quite easily the required thermal and acoustical performances, also enhancing the construction processand allowing for the final recycling of the components. In a warmer climate – such as the Italian one – a heat-conserving strategy has to be balanced against the potential overheating problems. Among the possible solutions, theuse of building-integrated Phase Change Materials, which could create a “light thermal inertia” (that is, without heavymass), was also investigated.

1. INTRODUCTIONDesigning the building of the future has become the real challenge of today. This means, in general, not only

designing high-tech, expensive and glazing rich buildings, but trying and give even popular buildings, low-costshousing, new technological practices to save energy and therefore to reduce air pollution. To assure to our cities and toour planet (the only one where we could live!) a future, we have to act today with real alternative solutions to sink downenergy consumption of all our houses.

For the first time in Italy, the “Passivhaus” concept has been introduced for a building of four flats, realised in theNorth of Italy. The concept is based on hyper-insulation, which creates an adiabatic behaviour of the living box: thismeans no heat flows from inside to outside, except for the hygienic necessary air exchange. State-of-the-art buildingtechnologies and installations were introduced, such as heat pumps fed by photovoltaic energy and domotic control ofall the devices. The house will be monitored from summer 2003 to summer 2004, in order to evaluate the actualperformance of the building: outsource energy consumption will be almost reduced to zero.

The construction of the building is based on steel primary frames with independent interior and exterior envelopes.Between them, installations run freely and the whole gap is filled by mineral wool as acoustic and thermal insulation.

The Passivhaus concept – and in general the intelligent use of energy – could be even more suited to warmerclimates (such as central and southern Italy), but these situation could require the presence of thermal inertia. This ispossible without adding significant weight to the construction by using PCM’s (Phase Change Materials) as an artificialinertial shield. Using the latent energy heat of PCM’s (salts or paraffins) protects from overheating the outsidelightweight cladding and the interior living spaces.

An evaluation campaign of these performances has been set parallel to the monitoring of the Passivhaus façadewithout PCM’s. In these experiments, will be used Climsel 32 salt (32°C melting point) packaged in aluminium smallbags. Future development of PCM’s in building industry will need shaped-form PCM’s to ease their application to theexisting construction products.

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Figure 1: the South front of the house: left, in its final appearance;right, during construction.

Figure 2: erecting one of the lightportal frames.

2. FUNCTIONAL MODELS FOR SUPER-EFFICIENT ENERGY BUILDINGSDesigning a highly-efficient energy building requires a correct relationship to the local climate, which should be

considered as a resource for the well being of the users instead of a hostile element.

The envelope of the building becomes an efficient filter between external and internal conditions, and has its own,intrinsic aptness for climatic control: this is the only way to reduce significantly the energetic consumption for winterheating and summer cooling, leaving to mechanical installations a role of fine-tuning the internal climate. Therelationship with the local climate being so close, every climate-sensitive building has to be specifically designed. Thereare no general rules valid in every situation.

One of the most interesting experiences with respect to minimising energy consumption for winter heating is theGerman one: here, a ten-year practice shows that it is possible, with limited technological and economical investment,to achieve a reduction in current energy consumption as large as 90% in comparison with a traditional building. Whenthe energy requirements for winter space heating are lower than 15 kWh/m² per year, the building is called aPassivhaus. The strategies adopted in Germany are mainly conservative, as in that climate the main issue is keepingheat inside the building.

On the contrary, the case study in Chignolo – the first example of such a low-energy building in Italy – wasconfronted with a milder winter and a hot and humid summer. The energetic strategy which was adopted was thereforemore articulated:

• the winter strategy is based on the conservation of heat inside the building, by a very performing envelope (highthermal resistance of opaque and transparent parts + air-tightness) and mechanical ventilation with heat recovery,which is anyway needed to maintain a good indoor air quality. These strategies allow for the full exploitation ofinternal heat gains (coming from people, luminaries, appliances and so on) and solar direct gains, which areallowed inside the building through south-facing windows. The energy which may still be required to keep theinterior comfortable can be supplied by heating the ventilation air through a small fan coil unit for each flat. Theseare fed with warm water produced by heat pumps for space heating and sanitary use;

• in summer, overheating is prevented by the effective shading of south-facing windows and by natural cross-ventilation. PV panels act as fixed overhang and protect the south side by direct solar radiation, while each windowhas a louvre system that can be adjusted by the users. In the event of high outside temperatures, fan coil units canbe fed with cold water produced by the heat pumps. The roof is also naturally ventilated to prevent heat from beingtransmitted to the attic.

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Figure 3: all the building components rely on Str/Enlight, layered technologies.

Figure 4: details of the hyper-insulated externalenvelope.

3. THE 1ST SUPER-EFFICIENT ENERGY BUILDING IN ITALY: THE CASE STUDY OFCHIGNOLO D’ISOLA

The building of Chignolo d’Isola stands in a residential area and is composed of four flats, two 60 m² and two 120m² large. Besides addressing the question of running energy needs, the building in Chignolo was realised with an eye onits performance all over the life cycle and on the well-being of its users: this is why it makes large use of dry buildingtechniques (Structure/Envelope, Str/En). This allows, first of all, for a very high internal comfort, as each apartment is akind of independent “box” inside a larger “box” which is the external envelope of the building. Moreover, Str/Entechniques present other different advantages. First of all, the construction operations are quicker, safer and cleaner thanwith traditional techniques, as the components are light, easy to work and there are no delays due to wet operations. Theenergy needed for construction, which contributes significantly to the overall embodied energy, is much lower incomparison with a traditional building (the house in Chignolo is eight times lighter than a comparable, massive one).Maintenance operations will also be greatly facilitated, as the building elements have reversible connections that allowfor the substitution of parts and the inspection of plants running in the walls. At the end of its life, the building will beeasily dismantled, with a selective, low-energy process, which will allow for the reuse, or the recycling, of itscomponents.

StructureThe structure of the building is composed by rolled-steel HEA 140 columns, which all but one stand on the perimeter

of the building in order to allow the future flexibility of the internal distribution. The border beams of the intermediatefloors and of the roof are made of cold-formed, C-shaped elements (350×70×35 mm, 7 mm thickness), where the joistsof the floors and the sandwich panels of the roof are fixed. The structure (columns and beams) was assembled on theground and subsequently erected with a small crane. The wind bracing of the structure in the vertical plane is realisedthrough steel elements (60×8 mm flat ones, or L-shaped 50×75×7 mm ones), while in the horizontal direction it relieson the plate behaviour of the dry floors.

Technological systemAs regards building technology, it is interesting to stress that Str/En technologies allow designing the components

for every single situation, by adding layers where higher performances are needed.

Vertical enclosures: perimeter walls are made up of two independent shells, which completely enclose the columns.Both envelopes stand on a zinc-coated steel stud structure, 75×50×0.6 mm large – the technique derives from the well-consolidated one of plasterboard walls. The external board is made with a fibre-reinforced, light cement board, 12.5 mmthick, waterproof and shock-resistant. A continuous layer in expanded polystyrene was put on its external face andfinished in render. The internal shell is a standard plasterboard wall on a steel sub-structure, including a vapour barrierlayer in aluminium. The resulting cavity was filled with mineral wool: the total thickness of the insulating layer reaches37 cm, with a thermal transmittance U lower than 0.1 W/m²K. The external envelope is thus practically adiabatic andthe energetic flow is concentrated on the transparent components, with a U-value of 1.1 W/m²K.

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Intermediate floors: the structure of the floors is composed of C-shaped, cold-formed steel joists, 250×50×20 mm indimension and 2 mm in thickness, which are bolted to the border beams by steel plates in order to have a reversibleconnection. The load-bearing part of the floor is completed by waterproof wooden panels, 28 mm thick, screwed on thejoists in order to take part in the horizontal wind bracing of the floor. The resistance to residential loads is thusguaranteed with a weight of just 40 kg/m². Over the load-bearing components, the other layers – required to meet designperformances – were simply laid by gravity, without a single drop of water being used. These layers are an insulatingone in polystyrene 20 mm thick, an acoustic one in mineral wool 10 mm thick, and two mineral boards which constitutethe rigid layer where the flooring is laid. Even though the floor is extremely light (100 kg/m²), the in-situ acousticalproofs have shown an insulation of 72 dB to aerial sound and a level of impact sound lower than 42 dB.

Roof: the copper-finished, ventilated roof was built by combining existing industrial products in innovative ways: inparticular, water-proofing and ventilation were obtained by directly fixing a corrugated sandwich panel to the structuralelements. The ridges create the space where air can flow by convection, and constitute the surface for fixing the woodenboarding where copper sheets are laid. A suspended plasterboard ceiling was installed below the insulated sandwichpanels: the wide resulting cavity was filled with 34 cm of rockwool, in order to dramatically reduce winter heat lossesand the incoming heat flow in summer. The rooms in the attic get their natural light from two couples of windows in thenorth and south façades and from eight skylights, with triple glass and U = 0.80 W/m²K.

Figure 5: Str/En technologies allow for the easyflowing of ducts in the cavities of walls and floors.

Figure 6: the tecnological installations at theunderground level: above, the ventilation unit with heat

recovery from exhaust air.

4. INSTALLATIONSA high energy-efficiency building requires the technological installation design to be strictly integrated to the

architectural and constructional issues, as it is only a holistic process that can take to a building which is in harmonywith the environment and its users. The dramatic reduction of current energy needs, which is obtained through simple,passive techniques, allows the use of small-scale, advanced system, using to large extents renewable energy.

In Chignolo, the production of hot water, for both heating and domestic use, and of cold water, for summer-timecooling, completely relies on a couple of heat pumps, working with low temperatures and small power. The combineduse of super-insulation and heat pumps, doing completely away with traditional combustion plants, avoids the emissionto the atmosphere of some 13,000 kg CO2 with respect to a comparable, traditional building.

Ducts and runs flow easily in the central wall of the building, and are finally distributed to the various flats throughthe cavities in walls and false ceilings. No pipes are installed between the layers of the floor, in order to maintain a highacoustical performance. Thanks to the use of Str/En building techniques, all the technical installations are easy toinspect, maintain and substitute.

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Table 1 – Design data.

Shape factor 0.576 Degree days 2,395Winter internal temperature +20°C (+1°C) External minimum temperature -6°CWinter internal HR Optional control Winter external HR 90%Temperature of water for heating +45/40°C Temperature of water for DHW +60/50°CWorking time 14 h/dayThermal power for heat losses 5.5 kW Thermal power for natural air change 1.6 kWTotal thermal power 7.1 kW Thermal power for summer cooling 16.5 kWDHW production 600 l/day Ventilation exchange rate 0.6 volumes/h

The functional scheme of the integrated ventilation and climatisation plant includes mechanical ventilation withcentral heat recovery from stale air, which allow the hygienic air change rate inside the flat without losing heat in theprocess. Local temperature in each flat can be adjusted by a small fan-coil unit, which heats or cool the internal air,according to the season.

These units are fed by water – both hot and cold – produced by the two reversible, air-to-water heat pumps, whichalso produce domestic hot water (DHW) on a separate circuit. This is possible also during the summer, when thecondensation heat from the chiller is completely re-used for DHW production. The use of heat pumps, thanks to thevery low energy needs, completely eliminates the need for fuel-consuming traditional installations. The pumps usepropane gas as cooling fluid, so avoiding the use of harmful, ozone-depleting CFC gases. Every heat pump has a thermalpower of 9.9 kW in winter and 12.5 kW in summer, while the overall electric power used by the two pumps together is9,000 kWh per year.

Table 2 – Heat pump characteristics.

Thermal power with external temperature –5°C 2 × 9.9 kWMaximum cooling power with external temperature 35°C 2 × 12.5 kWNominal absorbed electrical power 2 × 3.9 kWCOP in heating or DHW working mode 3.6COP in heating and DHW working mode 3.8EER in cooling only working mode 3.2EER in cooling and DHW working mode 6.8

The mechanical ventilation system of the flats is based on a central unit for air recirculation, with a heat recoverysystem with an efficiency of 74%. This unit takes fresh air outside the building, filters it, drives it through the heatexchanger – where it acquires the sensible heat of the outgoing stale air – and distributes it to the different flats. Thetotal quantity of treated air is 600 m³/h. In summer, the ventilation unit can by-pass the heat exchanger to improve thenight cooling of the flats by using fresh external air (only when its temperature is lower than the internal one). Exhaustinternal air is extracted from kitchens and bathrooms, so that unpleasant smells are eliminated before they diffuse in thenearby rooms.

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Figure 7: Functional model of the technological installations in Chignolo.

Inside each flat, a very advanced domotic system was installed. This links and co-ordinates all the systems of thehouse, such as artificial lighting, external shading, internal air thermostat, security, and so on. On the one hand, thissystem allows for an automatic management of the house in different situations, tuning the internal climate even whenthe inhabitants are not present; on the other, it allows to remote control the various components. The system, which ismodular and can be expanded and upgraded, can also link domestic and telecommunication appliances.

Clean energyA high energy-efficiency building allows for the effective exploitation of renewable energy sources, which are

available in limited quantities and, in a traditional building, cannot contribute significantly to the overall energeticbalance.

In Chignolo, a grid-connected photovoltaic (PV) system produces electricity. It is composed by a field of 36modules (31 m²) which give a nominal power of 3.96 kWp. PV panels are installed on the south façade, which receivesdirect solar radiation for most of the day, without obstructions, and are tilted 35° on the horizontal by a system ofaluminium elements cantilevering from the building. Every single-crystalline solar cell module (0.87 m²) guarantees apeak power of 110 Wp, with a nominal efficiency of 14.6%. As the expected production is 3,600 kWh per year, 40% ofthe total energy for climatisation and DHW production (that is, the energy required by the heat pumps) derives from acompletely renewable and non-polluting source.

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5. PCM’S IN OUTSIDE WALLSStratified layer lightweight building systems, based on Structure/Envelope (Str/En) construction techniques, proved

highly performing in continental climates (in general, hyper-insulated buildings are very suitable for mainly coldclimates but could suffer from overheating in warmer contexts).

The lack of inertia, due to the light weight of the building components, has brought to Phase Change Materials(PCM) in outside cladding, in order to give artificial thermal inertia to the building. PCM’s allow to sink down thetemperature of the outside walls by melting and using their own latent heat to store energy and delay heat transmission.

This solution is all the more interesting for climates where the winter insulation should not be so high, and where insummer the light weight wall would need a thermal inertial shield, to protect itself from overheating and sun irradiation.Following this inputs, a parallel campaign of testing and monitoring has been set up both on the wall of the houserealised in Chignolo d’Isola and on a number of test boxes with walls mixed by PCM.

This operation is a EU-funded research called C-TIDE (Changeable Thermal Inertia Dry Enclosures) and is a Craftproject inside the Fifth European Framework Program (FP5) aimed at fostering practical solutions for sustainabledevelopment. Partners of the research are PCQ, formed by Politecnico di Milano (BEST Department), University ofAncona (IDAU Department) and Politecnico di Torino, University of Gävle (Sweden) and 3 SME (Small and MediumEnterprises): Vanoncini (I), Poggi (I) and Climator (S).

Figure 8: Rendered view of the reference PCM wallto be tested in Ancona.

Figure 9: Theoretical simulation show that anexternal PCM layer helps smooth internal temperature

swing in the reference box.

As one of the partners (Climator) is a producer of PCM’s based on eutectic salts, these will be used for the testcampaign. This, starting 1st May 2003 and ending 15th September 2003, will evaluate the optimal position and quantityof ClimSel 32 salts (melting temperature 32°C) as outside shield in ventilated façade, in comparison to the one realisedin Chignolo’s Passivhaus, through a series of different reference boxes. The experimental field will be in Ancona, incentral Italy, where the summer climate will create heavy overheating situations on the external face of the envelopecomponents.

During the experimental campaign, samples of sandwich metal panels with PCM layers will also be tested, toprovide artificial thermal inertia also to these components. For this case, shape-formed PCM’s will be suitable andcontacts with Tsinghua University (China) will allow testing this new solution.

After evaluating all these performances for summer protection, a wintertime experimental campaign on the sameboxes will start to see the effects of the heat storage properties of PCM’s during the heating season (2003-2004). In thiscase, PCM’s will be placed both on the external façade (connected to heat vectors like water running in transmissiontubes) and in the internal layers, to use renewable energy or low-cost energy during the night (which is off-peak time).The application of shaped-form PCM’s in floors, ceilings or internal walls would be suggested and suitable.

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CONCLUSIONSBuilding the first Passivhaus represented a big step forward in the Italian construction sector. In fact, it shows how it

is possible to practically tackle the problem of energy consumption through hyper-insulated skins, high-performancewindows and integration of installations (heat pumps) with renewable energy sources (solar PV panels).

The design of building technologies – based on the Structure-Envelope concept – and installations ran parallel, werefollowed by scientists right from the beginning and will be evaluated during the next 1-year monitoring campaign.

A further development of intelligent energy use in houses is foreseen with the introduction of layers integratingPCM’s in dry, stratified building technologies. This could help both to delay overheating in façade and roofs and also tostore energy in internal partitions (floor or walls) during the winter.

A great potential for this application, which will be tested in an experimental monitoring campaign, is seen inshaped-form PCM’s, which could more easily fit together with the ordinary building construction elements now on themarket.

REFERENCES[1] Zambelli, E.; Imperadori, M.; Vanoncini, P.A. – Costruzione stratificata a secco, Maggioli editore, Rimini 1998.

[2] Imperadori, M. – Le procedure Struttura / Rivestimento per l’edilizia sostenibile, Maggioli editore, Rimini 1999.

[3] Imperadori, M. – Stratified layer building systems, Proceedings of CIB World Building Congress, Gävle, 1998.

[4] Lemma, M.; Imperadori, M. – Phase Change Materials in concrete building elements: performancecharacterisation, Proceedings of XXX IAHS World Housing Congress, Coimbra, 2002.

[5] Zambelli, E.; Masera, G. – Sustainable settlement in Mondovì: new standards for Italian housing, Proceedings ofXIX International Conference PLEA – Design with the environment, Toulouse, 2002.

[6] Feist, W. – Das Niedrigenergiehaus, C. F. Müller, Heidelberg 1998.

[7] Feist, W. – Das Passivhaus, C. F. Müller, Heidelberg 2000.

[8] Graf, A. – Das Passivhaus: wohnen ohne Heizung, Callwey, München 2000.

[9] Sommerliches Innenklima im Passivhaus-Geschoßwohnungsbau, CEPHEUS report no. 42, Passivhaus Institut,Darmstadt 2001.

[10] Feustel, H; Stetiu, C. – Thermal performance of Phase-Change Wallboard for residential cooling, published inCBS Newsletter, Fall 1997.

[11] Rudd, A. F. – Phase Change Material Wallboard for distributed thermal storage in buildings, published in theASHRAE Transactions: Research, Volume 99, Part 2, paper #3724, Atlanta 1993.